Fertilizing measures to decrease Norway spruce yellowing

At the end of nineties, within the mountain forests of the Krušné hory Mts., in connection with an increased acid deposition, the symptoms (yellowing) started to be visible, characterizing magnesium deficiency in the assimilation organs, when Mg contents were laying under 300 mg/kg. In mineral soil the Mg content is mostly less than 10 mg/kg. Contents of other basic elements (Ca, K) were also very low. During four years yellowing symptoms of the spruce stands have developed in an extent area of more that 10,000 ha. Since 1999, preventive measures have been adopted to improve the nutrition status of the forest stands. Liquid magnesium fertilizers as MgNsol, Lamag Mg, MgSsol were applied during the period of 1999-2002. Since 2001, in semi-operational experiment, powder Mg fertilizer - Silvamix F4 - of higher Mg content (63.3% MgO) was applied. Application of liquid fertilizer MgNsol has helped to compensate the nitrogen deficiency in the stands of insufficient nutrition in this element. Comparing of different types of liquid fertilizers has confirmed, that the highest increase of magnesium in assimilation organs was find in combined application of MgNsol and MgSsol fertilizers. Application of 300 kg/ha Silvamix F4 has increased the magnesium content in the first needle year class in 73% in average, potassium in 33%, calcium in 16%, and phosphorus in 85%. Besides increased nutrient content in needles also improvement of the health and phosphorus in 85%. Besides increased nutrient content in needles also improvement of the health state, i.e. revitalization of the stands affected can be observed.